The invention relates to a steering system for a motor vehicle, comprising a steering gear and at least one tie rod. The invention further relates to a method of controlling a vehicle, in which steerable wheels of the vehicle are acted upon.
Usually in a steering system, two tie rods are provided, which respectively extend between the steering gear and a steerable wheel of the vehicle. The two tie rods are arranged such that a steering trapezoid is formed, which causes the wheel on the inner side of the curve to receive a greater steering turning angle than the wheel on the outer side of the curve. In this way, it is attempted to fulfill as far as possible the Ackermann condition when double-tracked vehicles drive around bends. Through the effect of the transverse acceleration on the vehicle, on driving around bends, however, a floating angle occurs, so that the Ackermann condition is no longer valid. The wheel positions are therefore no longer adapted optimally to the driving situation.
Independently of these problems, efforts are made in modern vehicles to have an active effect on the driving behavior of the vehicle. The steering is also suitable for this, because it is a quick-acting actuating member with regard to the transverse dynamics of a vehicle. Therefore, efforts are made to stabilize a vehicle by means of controlled steering actions, without perception on the part of the driver, and/or to improve the transverse dynamic behavior of the vehicle in terms of automatic control. A known solution in steering systems with mechanical connection between steering gear and steering wheel is a so-called superimposed steering, in which an additional gear is provided between the steering wheel and the steering gear. The gear is provided with an actuating member, so that a steering correction can be produced, which is superimposed on the steering movement given by the driver via the steering wheel. The disadvantage of this solution consists in that the additional gear is situated at the steering column in a region in which usually no space is available. Another solution consists in a steer-by-wire steering system, in which merely an information technical connection exists between steering wheel and steering gear. The desired steering correction can be calculated in a simple manner by a control unit and superimposed electronically with the steering angle given by the steering wheel. The disadvantage of such a system consists, of course, in the high costs, because with a view to the necessary failure safety, the actors, sensors and processors must be constructed so as to be redundant. The disadvantage of both systems consists in that the angle position of the steered wheels to each other can not be adapted.